Clean Jersey 2.x method that is already implemented in 3.1

Signed-off-by: jansupol <jan.supol@oracle.com>
diff --git a/core-common/src/main/java/org/glassfish/jersey/internal/config/SystemPropertiesConfigurationModel.java b/core-common/src/main/java/org/glassfish/jersey/internal/config/SystemPropertiesConfigurationModel.java
index 13a4baf..6374f73 100644
--- a/core-common/src/main/java/org/glassfish/jersey/internal/config/SystemPropertiesConfigurationModel.java
+++ b/core-common/src/main/java/org/glassfish/jersey/internal/config/SystemPropertiesConfigurationModel.java
@@ -230,9 +230,4 @@
     public Set<Object> getInstances() {
         return null;
     }
-
-    // Jersey 2.x
-    private boolean hasProperty(String name) {
-        return getProperty(name) != null;
-    }
 }
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